Condenser



J1me 1951 Q R. H. CALDWELL 2,

CONDENSER Filed Sept. 30, 1949 3 Sheets-Sheet 1 E I INVENTOR A a/0 5 h. C74LDW6ZL ATTORNEYS June 1951 R. H. CALDWELL 2,556,838

INVENTOR. Paras /z CALDWELL J 1951 R. H. CALDWELL I 2, 5 ,838

CONDENSER Filed Sept. 30, 1949 s Sheets-Sheet s V INVENTOR. ADV/VS 6440/4 54 Patented June 12, 1951 UNITED STATES PATENT OFFICE CONDENSER Rufus H. Caldwell, Lake Katonah, N. Y. Application September 30, 1949, Serial No. 118,740

9 Claims.

This invention relates .to condensers and more particularly tovaria'b-le condensers wherein films of dielectric liquid are utilized between uniformly and closely spaced opposed surfaces of the rotor and stator thereof to provide maximum capacity with minimum space requirements and in which the dielectric consists solely of layers or films of the dielectric liquid. This application is a continuation-in-part of my prior application Serial No. 693,224, filed August 27, 1946, now abandoned.

An object of this invention is a radio condenser of simple and compact structure which has a high electrical efficiency, eliminates acoustical feedback and contact resistance, minimizes selfinductance, has high signal strength and sensitivity and is completely shielded.

A further object of this invention is a condenser of such construction that the electrically conductive portions thereof may be quickly and easily formed from the same batch of metal, thereby insuring complete uniformity.

Other objects, novel features and advantages of this invention will become apparent from the following specification and accompanying drawings, wherein:

Fig. 1 is a side elevation of a condenser embodying the invention;

Fig. 2 is an end view of Fig. 1;

Fig. 3 is a plan view of the condenser with the .cover removed;

Fig. 4 is a section partially broken away on the line 4-4 of Fig. l with the rotor rotated to its position out of the stator Wells;

Fig. 5 is a perspective view of a detail;

Fig. 6 is a side elevation of the rotor;

Fig. 7 is an end view of Fig. 6 looking in from the right, and

Fig. 8 is a bottom View of Fig. 6.

A body ll! of electrically conductive material preferably die-casting metal such, for example, as zinc alloy, is provided with a plurality of mounting projections H, provided with suitably tapped sockets I2. The body ii! is formed with two horizontal axis semi-cylindrical wells l3 and M separated by the partition I5. One end wall of the body is provided with a semi-circular recess l6 while the partition and the remaining wall are provided with semi-circular recesses 11 and 18, respectively. The upper surface of the body I6 is cut back along its periphery to form a shoulder Iii on which rests the periphery of a cover member 28 composed of the same material as the body. The end walls of the cover 20 are provided with semi-circular recesses complemental to the recesses it and H3. The partition I5 is provided with a groove 2| leading to the recess H.

A plate 22 is attached to one end of the body 10 and cover 20 by bolts 23 and has a hub 24 projecting through the circular opening formed between the body portion 10 and cover 20 bythe recess 18 and the complemental cove-r recess. A plate 25 is attached to the oppositeend walls of the body IQ and cover 28 by bolts 26, passing through holes in the plate and threaded into the body or cover. The plate 25 has an interior hub 21 received in the opening formed between the body portion I0 and the cover 20 by the recess [5- and the complemental cover recess. The bolt holes in the plates '22 and 25 are smooth and of somewhatlarger diameter than the diameter of the bolts 23 and 26 to permit slight adjustment of the plates 22 and 25 relative to the bolts.

A shaft 28 of insulating material such, for example, as a suitable plastic, has one end journaled in the hub 24 and is received in the partition recess I! and at its other end has a reduced diameter extension 29 journaled in and extending substantially beyond the plate 25. The shoulder of the shaft 28 engages the hub of the plate 2.5. The plate 25 is formed with a recessed exterior hub 31 and in the recess are provided a gasket .32 and a bearing A Washer 36 is held against the bearing 33 by a snap ring 35 seated in a peripheral groove 36 in the extension 29.

Two rotors 3! and 31a are fixed to the shaft 28 with the rotor 37! being located in the well i and the rotor 31a located in the well M. The rotor 3 is termed with an active arcuate surface 38 of slightly less radius than the radius of the well I3 and of slightly less maximum width than the width of said well.- At one end, the surface is of maxi-mum width and decreases toward its opposite end along a contour dependent on the condenser characteristics desired. The rotor also is provided on each side with an active segmental surface '39 adjacent the wide end of the surface .38 and located in slightly spaced relation to the well wall. The surfaces 38 and 39 are suitably designed to provide the proper active surfaces opposed to the active well surfaces to develop the desired capacity characteristics. The rotor 31a also is designed to provide the proper active surfaces opposed to the active well surfaces to develop the desired capacity characteristics which may differ from those of rotor .31. By active surfaces is meant those surfaces which determine the primary condenser capacity characteristics, e. g., other than strays.

A .bar 40 of insulating material is provided end 46a of a metal strip 46 having an aperture through which extends a bolt 41 threaded into the bar 40. Strip 46 is bent in such a manner between its aperture and its end 46a that the latter is biased toward the end of the bolt 41. A metal strap 48 electrically connects the rivet 43 to the bolt 41 so that the strip 46 is electrically connected to the contact arm 42. A thin plate 49 of insulating material is attached by a bolt 49a to the cover 20 in alignment with each groove 45 to be engaged by the end of a strip 46. The end 462) of the strip 46 constitutes a terminal for connecting the condenser in a circuit.

The wells l3 and I4 contain a fluid dielectric such, for example, as silicone fluid which is composed of heat stable organo-silica oxide polymers and has a high dielectric constant, such fluid being introduced into the body l before the cover is attached thereto. There is sufficient fluid dielectric used merely to immerse the rotors to a slight extent. However, rotation of the rotor causes a film of fluid to adhere to the entire active surface of each portion thereof as well as the entire active, surface of each of the stator wells. The spacing between the active surfaces of the rotors and the stator wells, which is maintained constant due to the structure above described and the assembly procedure described hereinafter, is made not more than and preferably less than twice the free film thickness of the dielectric fluid. Thus in any angular position of the rotor, the space between each active rotor surface and the corresponding opposed stator well surface is completely filled with the dielectric fluid and yet only a minimum amount of the fluid dielectric, that required to produce a free film on each of these surfaces, is required in the condenser. In one embodiment a silicone fluid having a viscosity of centistokes and a dielectric constant of 2.74 was found to have a free film thickness of 0.003 of an inch on a surface of die-cast zinc alloy, and the spacing between the active rotor and stator surfaces of the condenser was therefore fixed at approximately 0.005 of an inch. By free film thickness is meant the thickness of the fluid film which adheres to a given surface when the surface is dipped in the fluid and then removed therefrom, the excess fluid being allowed to drain off due to the force of gravity. This film thickness apparently depends upon the material of the surface, the viscosity of the fluid, and the surface tension. For any given surface material and any given fluid dielectric it can, however, be determined and the spacing between the active surfaces of the rotor and stator of my condenser then fixed as above.

The groove 2| provides for return to the wells of any fluid that may drop off the rotors and the shaft 28 is provided with a pin 50 to limit rotation of the shaft to less than 180 by engagement thereof with the partition [5.

In assembling the rotors with the body 10, th curved bottom surface of each well l3 and I4 is lined with a thin shim such, for. ex mple, as

a strip of paper. The shaft 26, assembled with the rotors 31 and 31a. and with the plates 22 and 25 and the accompanying gaskets and bearings, is placed in the body In with the rotor surfaces engaging the shims. The bolts 23 and 26 are put in place and tightened so that a definite relation is established between the rotor surfaces and the well surfaces by reason of the interposed shims. This operation is facilitated by having the bolt holes in the plates 22 and 25 of slightly larger diameter than the bolts. After the bolts have been set, the shims are removed by rotating the shaft 21 and pulling on the shims themselves, thereby leaving a space between the surfaces of the rotors and the well surfaces equal to the thickness of the shim. With this arrangement, an accurate gap may be established between the opposing active surfaces, whose value, as described above, is not greater than twice the free film thickness of the fluid dielectric to be used. The cover 20 is now put in place and a tight seal between the cover and body is obtained by applying sealing material along the juncture of the two units.

In use of the condenser above described, the body [8 is mounted upon a suitable support by means of bolts threaded into the sockets I2 and through such connections the body I0 is grounded. Conductors are connected to the terminals 46b which in turn are electrically connected to the rotors 31 and 31a through the members 4-2. The rotors 31 and 31a are electrically insulated from the enclosure and from each other by the plastic material shaft 28. Each rotor is included in a circuit separate from the circuit including the other rotor but the enclosure is common to both circuits. A suitable handle or other operating member is connected to the section 29 of the shaft 28 for rotating the shaft 28 and the rotors mounted thereon.

The portion 46a of the strip 46 in combination with the insulating material plate 49' and the enclosure constitutes a trimming condenser as an integral part of the fluid condenser. The capacity of the trimming condenser may be varied by adjustment of the bolt 41 to vary the area of contact between the strip portion 46a and the insulating material plate 49.

In the manufacture of the above-described condenser, the body, cover and 'rotors are simultaneously die cast in a single mold from the same batch of die-casting metal which preferably is zinc alloy. The casting of the base, cover and rotors in a single operation of this kind insures absolute uniformity in the material of which they are composed.

In the condenser above described, the solid cam rotors may be provided with scientifically developed areas and contour separated from the stator by fixed increments of clearance. The relatively large balanced cam rotor cast with only one moving part removes the chief causes of acoustical feed-back present in multiple plate constructions in which it is practically impossible to avoid vibration of the plates. Self-inductance is minimized and the passage of much higher frequencies and volume is permitted. The fluid dielectric, together with the inherent characteristics of the cam rotor design greatly reduces contact resistance and produces an improved electrical efficiency up to nearly twice that of an air gap multiple plate condenser. Strength of signal and sensitivity are correspondingly increased. The low loss plastic shaft also contributes to the increased efliciency. Furthermore, the condenser is of sealed-in construction and is dust-proof, moisture-procf and moldproof. It constitutes an accurately positioned long-life assembly that cannot be damaged or jolted out of adjustment during assembly thereof in a radio set or in transportation.

While the condenser has been herein disclosed as a two-stage capacity, it is to be understood that it may be of a single-stage or multiple-stage capacity as desired. Although silicone fluid is specifically disclosed as the fluid dielectric, other fluids of suitably high dielectric constants may be used. Silicone fluid is particularly well fitted for use as the fluid dielectric because it has a high dielectric constant and remains permanently stab-1e without breaking down or viscosity change when subjected to temperature extremes and when used throughout a long life of service. Furthermore, it is to be understood that various changes may be made in the structure above described, without in any way departing from the spirit of the invention as defined in the appended claims.

What is claimed is:

1. A condenser comprising an electrically conductive semi-cylindrical well, an electrically conductive rotor having an arcuate surface having a radius less than the radius of the inner arcuate surface of said well, journals for said rotor disposed on the axis of said well, said rotor including bearing surfaces on either side thereof cooperating with said journals for rotation of said rotor within said Well in a fixed spaced relationship between the cooperating arcuate surfaces thereof, insulation disposed between said well and said rotor, a film of dielectric liquid adhering to and covering said inner arcuate surface of said well, and a film of the same dielectric liquid adhering to and covering said cooperating arcuate surface of said rotor, the difference between the respective radii of said arcuate surface of said well and said arcuate surface of said rotor being less than twice the free film thickness of the dielectric liquid, whereby in all positions of the rotor the dielectric films completely fill the space between the contiguous opposed portions of the closely spaced arcuate surfaces of said well and rotor with a fluid dielectric of uniform thickness.

2. Apparatus according to claim 1 wherein the dielectric liquid comprises silicone fluid composed of heat stable organo-silica oxide polymers.

3. Apparatus according to claim 1 in which the well and rotor are composed of identical diecast material.

4. A condenser comprising an electrically conductive semi-cylindrical well, an electrically conductive rotor having an arcuate surface having a radius less than the radius of the inner arcuate surface of said well, an insulating shaft for said rotor journaled in and on the axis of said well for rotation of said rotor therein in a fixed spaced relationship, a film of dielectric liquid adhering to and covering said inner arcuate surface of said well, and a film of the same dielectric liquid adhering to and covering said cooperating arcuate surface of said rotor, the difference between the respective radii of said arcuate surface of said well and said arcuate surface of said rotor being less than twice the free film thickness of the dielectric liquid, whereby in all positions of the rotor the dielectric films completely fill the space between the contiguous opposed portions of the closely spaced arcuate surfaces of said well and rotor with a fluid dielectric of uniform thickness.

5. A condenser comprising an electrically conductive enclosure having a semi-cylindrical well, an electrically conductive rotor having an arcuate surface having a radius less than the radius of the'inner arcuate surface of said well, journals for said rotor disposed on the axis of said well, said rotor including bearing surfaces on either side thereof cooperating with said journals for rotation of said rotor within said well in a fixed spaced relationship between the cooperating arcuate surfaces thereof, insulation disposed between said well and said rotor, a film of dielectric liquid adhering to and covering said inner arcuate surface of said well, and a film of the same dielectric liquid adhering to and covering said cooperating arcuate surface of said rotor, the difference between the respective radii of said arcuate surface of said well and said arcuate surface of said rotor being less than twice the free film thickness of the dielectric liquid, whereby in all positions of the rotor the dielectric films completely fill the space between the contiguous opposed portions of the closely spaced arcuate surfaces of said well and rotor with a fluid dielectric of uniform thickness.

6. Apparatus according to claim 5 wherein the dielectric liquid comprises silicone fluid composed of heat stable organo-silica oxide polymers.

7. Apparatus according to claim 6 including a reservoir pool of said dielectric liquid in the bottom of said well.

8. Apparatus according to claim 5 including a reservoir pool of said dielectric liquid in the bottom of said well.

9. A condenser comprising an electrically conductive enclosure having a semi-cylindrical well, en electrically conductive rotor having an arcuate surface having a radius less than the radius of the inner arcuate surface of said well, an insulating shaft for said rotor journaled in and on the axis of said well for rotation of said rotor therein in a fixed spaced relationship, a film of dielectric liquid adhering to and covering said inner arcuate surface of said well, and a film of the same dielectric liquid adhering to and covering said cooperating arcuate surface of said rotor, the difference between the respective radii of said arcuate surface of said well and said arcuate surface of said rotor being less than twice the free film thickness of the dielectric liquid, whereby in all positions of the rotor the dielectric films completely fill the space between the contiguous opposed portions of the closely spaced arcuate surfaces of said well and rotor with a fluid dielectric of uniform thickness.

RUFUS I-I. CALDWELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,589,204 Miller June 15, 1926 1,641,314 Bradley Sept. 6, 1927 1,746,967 Reid Feb. 11, 1930 1,968,772 Kenney July 3'1, 1934 2,273,522 Horowitz Feb. 17, 1942 2,384,384 McGregor Sept. 4, 1945 FOREIGN PATENTS Number Country Date 483,487 Great Britain Apr. 19, 1938 

